Project Summary Aortic aneurysms (AA) represent a significant clinical problem with a high risk of aortic rupture leading to sudden death. Currently, there are no medical therapies available to treat aneurysms and a clear understanding of the pathobiology of AA formation is key to develop therapeutic pharmacological approaches. Recent studies reveal that ATP can be released by cells in a controlled manner through pannexin 1 (Panx1) channels to signal through purinergic P2X or P2Y receptors. ATP is a nucleotide released in large amounts after tissue injury such as AA and serves as a ?danger signal? to mediate inflammation. Our data suggest that Panx1 on endothelial cells (ECs) is an important mediator of vascular inflammation in a murine model of abdominal AA (AAA) and can be a major source of extracellular ATP. The expression of Panx1 is highest in the arterial network especially in the aortic endothelium. The scientific premise of this proposal focuses on the crosstalk between aortic endothelium, smooth muscle cells and relevant immune cells to delineate Panx1- mediated signaling in AAA progression. Thus, this proposal will test the overall hypothesis that EC Panx1 signaling is a major, early inflammatory mediator of the signaling cascade via release of ATP resulting in smooth muscle cell activation, leukocyte infiltration and vascular inflammation. Using novel inducible cell- specific genetic knockout animals, specific pharmacological Panx1 inhibitors and P2X/P2Y antagonists, we will delineate this previously unknown mechanism of AAA pathobiology. Aim 1 will determine if EC Panx1 signaling mediates AAA via ATP release and its crosstalk with aortic smooth muscle cells as well as to determine whether the P2X7 receptor is a major determinant of AAA. We will also investigate if Panx1 inhibition can treat preformed AAAs in the murine models. Aim 2 will determine if Panx1 signaling mediates leukocyte activation and infiltration during AAA. The role of Panx1 and specific purinergic receptors on macrophages will be deciphered as well as whether Panx1 mediates neutrophil transendothelial migration. Aim 3 will determine if pharmacologic inhibition of Panx1 or specific P2 receptors will treat AAA using a chronic inflammatory, large animal porcine AAA model. Our studies will provide novel insight into mechanisms of molecular signaling interactions between aortic endothelial cells, smooth muscle cells, and immune cells (macrophages and neutrophils), to define Panx1 as a novel therapeutic target for the treatment of AAs.